The present invention relates to large-screen visualizing devices in which the image which has been displayed on a visualization cell is projected onto a screen. Such a device enables a television image for example to be displayed without using a cathode-ray tube.
It is known to use for this a liquid crystal cell described in the U.S. application Ser. No. 902,112 filed on May 2, 1978, now U.S. Pat. No. 4,202,010, granted on May 6, 1980 in the name of Hareng et al. In this device, the television image is recorded line by line in a smectic liquid crystal layer by using heating lines for bringing the liquid crystal into an isotropic phase. On the return of the liquid crystal to the smectic phase, it is more or less diffusing depending on the electrical voltage representative of the video signal which is applied along the heating line. The dimensions of such a cell are necessarily limited, with a side of the order of 1 cm, and it is necessary in order to obtain an image of the size of that given for example by a cathode-ray tube, to effect an optical projection of this image on a screen. Whatever the optical systems used the bulkiness in depth of the projection device is far from being negligible. On the whole, the overall dimensions of the device comprising the cell, the projection system and the screen are of the order of those of a cathode-ray tube.
These latter years there has been developed, under the generic term of distributed optics, a screen projection device having a small depth. For that, the original image is exploded into a multitude of small pieces which are each projected by a single lens onto a screen. The whole of the system is designed so that on this screen the lines separating the different pieces of the image are substantially invisible. In its original version, this system was purely optical and a description of it can be found in the U.S. review: "Journal of Applied Photographic Engineering", Vol. 3, No. 4, 1977, pages 221-224.
In the issue of Aug. 3, 1978 of the U.S. review "Electronics", it was proposed replacing the small image pieces of this device by liquid crystal cells. Thus is obtained a large-screen visualization device, by optical projection from liquid crystal cells, which has a small depth. However, this description is very sketchy and in particular the system for illuminating the liquid crystal cells is without change in relation to the original optical device and is relatively complicated and costly.